Medical professionals commonly use catheters for gaining prolonged access to an area within the body. Once the catheter tip is positioned at the target location, treatments such as antibiotics, chemotherapy, pain medicine, and nutrition can be administered. If the catheter tip is improperly positioned during insertion, various risks to the patient arise, including a fluid infusion that causes pain or injury to the patient, complications due to increased thrombosis rates, delays in therapy, catheter malfunction and additional costs.
General standards for proper catheter insertion depend on the type of catheter and the treatment being provided. For example, peripherally inserted central catheters (or PICC lines) are commonly inserted into a brachial, cephalic or basilic vein in the arm and advanced through the venous system towards the superior vena cava (SVC). Current medical standards recommend that the distal tip of the catheter terminate in the lower ⅓ of the SVC, close to the junction of the SVC and the right atrium (RA). However, since PICCs are commonly inserted into a vein in the arm and advanced through the venous system to reach the SVC, the PICC line tip may be inadvertently positioned in a non-target area, such as the internal jugular, the subclavian vein, or too far past the SVC-RA junction and into the heart.
Catheter tip location techniques have improved the ability of medical professionals to verify the location of the catheter tip. One technique uses fluoroscopy to confirm tip location. Fluoroscopy provides the operator with real-time images of the patient's anatomy using a fluoroscope. Another technique uses a combination of an electromagnetic beacon and an electromagnetic detection element to track the beacon positioned near the catheter tip. Many techniques have also been described for using electrocardiography (ECG) to assist with catheter tip placement by measuring an ECG signal from an intravascular (IV) electrode positioned at or near the catheter tip.
Tracking ECG waveform changes measured from an IV electrode as the catheter advances through the vasculature towards the SA node can provide valuable feedback to the medical professional placing the catheter, since the SA node is located near the SVC-RA junction. Specifically, tracking the P-wave morphology is known to be a valuable tool. For example, as the IV electrode advances down the SVC towards the SA node, the amplitude of the P-wave will start to rise. The amplitude of the P-wave will eventually peak when the IV electrode is closest to the SA node, and eventually start to decrease in amplitude as the IV electrode moves away from the SA node and enters the RA. Observation of this phenomenon has been utilized by medical professionals for catheter placement procedures at least as early as the mid-20th century.
Automated systems that track P-wave morphology for catheter tip placement have also been previously described. For example, in U.S. Pat. No. 5,121,750 to Katims, incorporated herein by reference, a monitoring system detects changes in the P-wave as measured from an IV electrode for providing automated user instructions on catheter placement. The monitoring system (1) detects increases in the P-wave amplitude as the IV electrode approaches the SA node and signals the user to continue advancing the catheter, (2) detects a decrease in the P-wave amplitude as the IV electrode passes the SA node and signals the user to pull back the catheter, and (3) detects that the P-wave is within a certain range of the maximum and signals the user to stop once within that range.
For tip positioning systems that rely on tracking changes in P-wave amplitude for providing user feedback, several obstacles may arise. For instance, P-wave location and morphology can change from patient to patient based on a number of factors (explained in further detail below). It would be beneficial for an ECG and P-wave based tip location system to have a more patient specific analysis approach to account for patient-to-patient variability. Further, ECG signals from IV electrodes tend to have low resolution due to a number of factors, including electrode downsizing and design limitations, movement, and pickup of physiologic and extraphysiologic artifacts. A noise spike may cause the algorithm to misinterpret the acquired signal, possibly leading to erroneous user feedback. Systems that can accurately provide user feedback, manage lower resolution IV electrode signals, and minimize the influence of ECG artifacts on signal processing would be advantageous.
Further, problems such as thrombus buildup at the catheter tip and within the catheter lumen can affect IV ECG signal acquisition. Thrombus buildup can partially block electrode exposure which can result in a muted signal. Further, thrombus buildup in contact or near the electrode can cause the IV ECG signal to refract off of the thrombus formations, adding noise to the IV ECG waveform. To clear the catheter lumen and opening of thrombus, and to combat the formation of new thrombus, the catheter lumen can be flushed with saline. However, this can add time and cost to the procedure. Further, prolonged interruptions in catheter advancement may interfere with the normal execution of the tip location algorithm, and may prevent the algorithm from properly executing, or lead to erroneous user feedback.
Improved catheter tip placement systems and methods for overcoming these issues is desired.